The broad objective of this program project proposal is to maintain two different groups of genetically defined mice under highly controlled laboratory conditions and assess cross-sectional samples of these mice on a variety of age-related behavioral, immunological, physiological, neurobiological, and pathological processes at three ages, representing young adulthood, midlife and old age. Longevity will be determined in a separate group. These animals-recombinant inbred (RI) strains derived from the C57BL/6 and DBA/2 inbred strains and an F2 generation derived from these same progenitor strains-- are complementary elements in a two-phase program of identify chromosomal locations of genes ("quantitative trait loci" or QTLs) that influence complex age-related traits. The localization of such QTLs will open up valuable research approaches both to the reductionist explorations of the mechanisms of aging processes, and also the integrative science relating interactions among genes and between genes and environmental factors in influencing the phenomena of aging.